Chen Weijie

Semitransparent selenium solar cells are reported with a champion state-of-the-art performance efficiency of 5.2% when illuminated through the carrier-separating junction and 2.7% when illuminated from the opposite side of the device. Varying the Se thickness shows a narrow optimal selenium thickness of ≈300–500 nm for both illumination directions. Inverting the typically reported architecture is encouraged for tandem fabrication.

Trigonal selenium (Se) is an elemental, direct-bandgap (1.95 eV) semiconductor with a low processing temperature, which could be a suitable top absorber for tandem solar cell applications. For incorporation in tandem architectures, both sides of the Se cell should be semitransparent. However, all reported Se solar cells have metallic back contacts. To demonstrate the potential feasibility of Se as a wide-bandgap absorber for tandems, herein, bifacial single-junction selenium solar cells with device areas above 0.4 cm² are reported. When illuminating through the n-type contact, the bifacial cell power conversion efficiency (PCE) is 5.2%, similar to a standard monofacial cell. The efficiency is lower (2.7%) when illuminating through the p-type contact, which is attributed to low carrier diffusion lengths and lifetimes in selenium. This suggests the necessity to invert the typical single-junction device structure when incorporating it into a tandem device.

In this study, efficient inverted organic photovoltaics using hexagonal boron nitride as an electron blocking layer is fabricated and the device stability, as compared to the reference devices, is improved.

Abstract

In this study, monolayer hexagonal boron nitride (h-BN) grown via chemical vapor deposition (CVD) as an effective electron blocking layer (EBL) for the organic photovoltaics (OPVs) is proposed. Unexpectedly, it is found that h-BN can replace the commonly used hole transport layers (HTLs), i.e., molybdenum trioxide (MoO₃) and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) in an inverted device architecture. Here, a wet-transfer technique is employed and a single layer of h-BN on top of the PV2000:PC₆₀BM blend is successfully placed. Analysis of the bandgap diagram shows that the monolayer h-BN makes smaller barrier for holes but significantly larger barrier for electrons. This makes the h-BN effective in blocking electrons while creating a possible path for the holes through tunneling to the electrode, due to the low energy barrier at the PV2000/h-BN interface. Using h-BN as an EBL, efficient inverted OPVs are achieved with an average solar-to-power conversion efficiency of 6.13%, which is comparable with that of reference devices based on MoO₃ (7.3%) and PEDOT:PSS (7.6%) as HTLs. Interestingly, the devices with h-BN shows great light-soak stability. The study reveals that the monolayer h-BN grown by CVD could be an effective alternative EBL for the fabrication of efficient, lightweight, and stable OPVs.

A novel strategy is developed for preparing high-efficient perovskite solar cells (PSCs) with ferroelectricity by incorporating 1D ferroelectric perovskite with 3D organic–inorganic hybrid perovskite (OIHP). The 1D/3D mixed OIHP films exhibit evident ferroelectricity, and the 1D perovskite is randomly distributed. The poling of the 1D/3D mixed PSCs increase V _oc, and the ferroelectric-polarization is retained for a long time.

Abstract

With the capability to manipulate the built-in field in solar cells, ferroelectricity is found to be a promising attribute for harvesting solar energy in solar cell devices by influencing associated device parameters. Researchers have devoted themselves to the exploration of ferroelectric materials that simultaneously possess strong light absorption and good electric transport properties for a long time. Here, it is presented a novel and facile approach of combining state-of-art light absorption and electric transport properties with ferroelectricity by the incorporation of room temperature 1D ferroelectric perovskite with 3D organic–inorganic hybrid perovskite (OIHP). The 1D/3D mixed OIHP films are found to exhibit evident ferroelectric properties. It is notable that the poling of the 1D/3D mixed ferroelectric OIHP solar cell can increase the average V _oc can be increased from 1.13 to 1.16 V, the average PCE from 20.7% to 21.5%. A maximum power conversion efficiency of 22.7%, along with an enhanced fill factor of over 80% and open-circuit voltage of 1.19 V, can be achieved in the champion device. The enhancement is by virtue of reduced surface recombination by ferroelectricity-induced modification of the built-in field. The maximum power point tracking measurement substantiates the retention of ferroelectric-polarization during the continued operation.

A ligand molecule containing carbonyls (carboxyl and amide) and a long hydrophobic alkyl chain is incorporated into a perovskite precursor to achieving improved crystallinity, reduced trap state density, and inhibited ion migration. This strategy enables an impressive power conversion efficiency exceeding 23% with inhibited hysteresis.

Abstract

The nonradiative recombination losses resulting from the trap states at the surface and grain boundaries directly hinder the further enhancement of power conversion efficiency (PCE) and stability of perovskite solar cells. Consequently, it is highly desirable to suppress nonradiative recombination through modulating perovskite crystallization and passivating the defects of perovskite films. Here, a simple and effective multifunctional additive engineering strategy is reported where 11 Maleimidoundecanoic acid (11MA) units with carbonyls (carboxyl and amide) and long hydrophobic alkyl chain are incorporated into a perovskite precursor solution. It is revealed that improved crystallinity, reduced trap state density, and inhibited ion migration are achieved, which is ascribed to the strong coordination interaction between the carbonyl groups at both sides of 11MA molecules and Pb²⁺. As a result, improved efficiency and stability are achieved simultaneously after introducing 11MA additive. The device with 11MA additive delivers a champion PCE of 23.34% with negligible hysteresis, which is significantly higher than the 18.24% of the control device. The modified device maintains around 91% of its initial PCE after aging under ambient conditions for 3000 h. This work provides a guide for developing multifunctional additive molecules for the purpose of simultaneous improvement of efficiency and stability.

A mesoporous charge-transporting layer is embedded into quasi-interdigitated back-contact perovskite devices. The increased interfacial contact area significantly enhances the charge extraction behavior leading to a record high current density of 21.3 mA cm⁻² on a back-contact perovskite device.

Abstract

As the performance of organic–inorganic halide perovskite solar cells approaches their practical limits, the use of back-contact architectures, which eliminate parasitic light absorption, provides an effective route toward higher device efficiencies. However, a poor understanding of the underlying device physics has limited further performance improvements. Here a mesoporous charge-transporting layer is introduced into quasi-interdigitated back-contact perovskite devices and the charge extraction behavior with an increased interfacial contact area is studied. The results show that the incorporation of a thin mesoporous titanium dioxide layer significantly shortens the charge-transfer lifetime and results in more efficient and balanced charge extraction dynamics. A high short-circuit current density of 21.3 mA cm^–2 is achieved using a polycrystalline perovskite layer on a mesoscopic quasi-interdigitated back-contact electrode, a record for this type of device architecture.

Rapid degradation of ion migration, measurement source‐induced damage, phase transition, and separation of perovskite materials hinder accurate evaluation by conventional characterization tools. Recent advanced characterization tools, such as cryogenic temperature assisted measurement, in situ observation, and multidimensional imaging/mapping are presented here that enable the correct diagnose perovskite properties.

Abstract

In the last 10 years, organic–inorganic hybrid perovskite solar cells have achieved unprecedented advances, to the point where they now exhibit extremely high efficiency. However, long‐term stability and areal scalability limitations impede the commercial application of perovskite materials, and appropriate diagnosistic tools have become necessary to evaluate perovskite materials. Characterization of perovskite materials is regularly misinterpretated, due to unique intrinsic and extrinsic factors: degradation from the measurement source, ion migration, phase transition, and separation. Herein, studies on perovskites are reviewed that have used advanced characterization tools to overcome characterization challenges. Cryogenic temperature assisted measurements mitigate degradation or phase transitions induced by the measurement source. In situ measurements can track the variation of perovskite materials depending on external stimuli. Spatial material properties are able to be evaluated by the use of multidimensional mapping techniques. An overview of these advanced characterization tools that can overcome the challenges associated with established tools provides the opportunity for further understanding perovskite materials and solving the remaining challenges on the road to commercialization.

The power conversion efficiencies (PCEs) of single‐junction organic solar cells have now reached over 18%. Recent progress that has been made in understanding the morphology and the device photophysics of high performing polymer:non‐fullerene acceptor blends and some of the major challenges that must be overcome to attain PCEs of over 20% are highlighted.

Abstract

The power conversion efficiencies (PCEs) of single‐junction organic solar cells (OSC) have now reached over 18%. This rapid recent progress can be attributed to the development of new nonfullerene electron acceptors (NFAs) that are paired with suitable high performing polymer electron donors. Substantial improvements in the PCEs and long‐term stability enabled by NFA OSCs have allowed the development and integration of these systems into many niche and novel applications. Here, the recent progress that has been made in understanding the device photophysics of high performing polymer:NFA blends is highlighted. As the bulk heterojunction morphology is intrinsically linked to the device photophysics, this review focuses on studies that have provided noteworthy morphological insights using advanced techniques such as solid‐state NMR and resonant soft X‐ray scattering. Through this, some of the major challenges that must be overcome to attain PCEs of over 20% in NFA OSCs are addressed.

The effects of post treatments of thermal annealing (TA) and solvent annealing (SVA) on morphology evolution and efficiency are systematically investigated. The results show that CS₂ annealing induces better molecular interconnection and lower non-radiative recombination than that of TA treatment, which enables the best voltage and fill factor improvements and gives a record efficiency of 15.39%.

Abstract

Post-treatment is of great importance to form nanoscale phase-separated morphology for all-small-molecule organic solar cells (ASM-OSCs), while the reasons for the difference between thermal annealing (TA) and solvent annealing (SVA) remain unclear. In this work, the influences of TA and SVA (with three common solvents of THF, CS₂, and CF) are systematically investigated based on BT-2F:N3 through characterization of photovoltaic performance, molecular stacking, charge transfer, etc. The results indicate that: i) solvents with good solubility induce stronger molecular interaction than that of TA treatment, and thus endowing molecules with better mobility to migrate for crystallization and phase separation, which leads to better J-aggregation and molecular interconnection. ii) Donor-selectively dissolved CS₂ is better for optimizing the donor domain for its suitable domain size, improved molecular interaction and interconnection, and reduced trap states. iii) CS₂ imposes a small impact on N3 acceptors and thus alleviates the increment of non-radiative recombination. As a result, CS₂ SVA with unique multifunctions enables a PCE of 15.39% with simultaneously improved voltage (0.845 V) and fill factor (75.02%), which is much higher than 14.66% of TA treatment. Moreover, 15.39% efficiency is also the highest value in binary ASM-OSCs.

In this work, tandem solar cells using wide bandgap hydrogenated amorphous silicon and narrow bandgap organic bulk heterojunction photovoltaics are explored. By chemically texturing transparent conductive oxide layers, the current matching between two subcells can be optimized to give a power-conversion efficiency of 15% while greatly improving operational stability compared to single junction organic photovoltaics.

Abstract

Monolithically stacked tandem solar cells present opportunities to absorb more of the sun's radiation while reducing the degree of energetic loss through thermalization. In these applications, the bandgap of the tandem's constituent subcells must be carefully adjusted so as to avoid competition for photons. Organic photovoltaics based on nonfullerene acceptors (NFAs) have recently exploded in popularity owing to the ease with which their electrical and optical properties can be tuned through chemistry. Here, highly complementary and efficient 2-terminal tandem solar cells are reported based on a wide bandgap amorphous silicon absorber, and a narrow bandgap NFA bulk-heterojunction with power conversion efficiencies (PCEs) exceeding 15%. Interface engineering of this tandem device allows for high PCEs across a wide range of light intensities both above and below “1 sun.” Furthermore, the addition of an inorganic silicon subcell enhances the operational stability of the tandem by reducing the light-stress experienced by the bulk heterojunction, resolving a long-standing stumbling block in organic photovoltaic research.

This review aims to discuss challenges and recent advances in all-inorganic perovskites for advanced photovoltaics. After discussing the structural and electronic properties of the materials, the focus of this review moves towards all-inorganic perovskite solar cells, reporting the most effective approaches to improve device performance. Finally, efforts and challenges toward the fabrication of all-inorganic perovskite solar modules are discussed.

Abstract

In the last ten years, organic–inorganic hybrid perovskites have been skyrocketing the field of innovative photovoltaics (PVs) and now represent one of the most promising solution for next-generation PVs. Within the family of halide perovskites, increasing attention has been focused on the so-called all-inorganic group, where the organic cation is replaced by cesium, as in the case of CsPbI₃. This subclass of halide perovskites features desirable optoelectronic properties such as easily tunable bandgap, strong defect tolerance, and improved thermal stability compared to the hybrid systems. When integrated in PV cells, they exhibit high power conversion efficiency (PCE) with record values of 19.03%. However, all-inorganic perovskite solar cells (PCSs) face several challenges such as i) instability of the CsPbI₃ photoactive phase in ambient conditions, ii) inhomogeneous film morphology, and iii) high surface defect density. This work focuses on the mentioned challenges with a special attention on discussing the Cs–Pb–X system (X = I, Br). Then, the most recent and effective approaches for increasing both the PCE and the stability of devices are reviewed, which include material doping, interface engineering, and device optimization. Finally, the first efforts toward the upscaling of Cs-based PSCs, and predicted methods for enabling large-scale production, are discussed.

The dominant deep defect states in freshly prepared CsPbI_{3− x} Br _x films are mainly antisite defect pairs (Pb_I and I_Pb) and interstitial defects (Pb_i). All these defects are reduced because of self-regulation process after resting the films overnight in the dark. Based on this strategy, the reduced-defect high quality CsPbI_{3− x} Br _x films can be obtained and thus higher photovoltaic performance.

Abstract

Deep defects often act as Shockley–Read–Hall recombination centers in semiconductor materials, degrading the photoelectric performance and long-term stability of assembled photovoltaic devices. In this report, deep level transient spectroscopy is probed to determine defect concentrations and defect energy levels in all-inorganic CsPbI_{3− x} Br _x perovskite solar cells. Combining that data with the density functional theory calculation, the dominant deep defect states are assigned to antisite defect pairs (Pb_I and I_Pb) and interstitial defects (Pb_i) in freshly prepared CsPbI_{3− x} Br _x films. Astonishingly, all these defects are reduced by approximately one or two orders of magnitude after resting the films overnight, in excellent agreement with the defect-reduced trends from the fluorescence spectra, transient photovoltage, and space-charge-limited current measurements. The reduced defect concentrations are proposed to be connected with their self-regulation during the storage. To assess the thermodynamics possibilities, two reaction procedures are designed to calculate their formation enthalpies and negative Gibbs energy change revealed their spontaneous processes. Then, strain relief is the direct driving force for ion migration, thus defect-regulation by tracing the X-ray diffraction patterns. Furthermore, the power conversion efficiency is improved and the J–V hysteresis is suppressed due to reduced ion migration via relaxed strain.

A novel multi-selenophene-containing polymer acceptor PFY-3Se with a narrow band gap, high electron mobility, and improved intermolecular interaction was developed. In all-polymer solar cells, batch-to-batch insensitive PFY-3Se obtained an impressive power conversion efficiency (PCE) of over 15 % with high reproducibility, which is much better than its analogue, selenophene-free PFY-0Se (13.0 %).

Abstract

All-polymer solar cells (all-PSCs) progressed tremendously due to recent advances in polymerized small molecule acceptors (PSMAs), and their power conversion efficiencies (PCEs) have exceeded 15 %. However, the practical applications of all-PSCs are still restricted by a lack of PSMAs with a broad absorption, high electron mobility, low energy loss, and good batch-to-batch reproducibility. A multi-selenophene-containing PSMA, PFY-3Se, was developed based on a selenophene-fused SMA framework and a selenophene π-spacer. Compared to its thiophene analogue PFY-0Se, PFY-3Se shows a ≈30 nm red-shifted absorption, increased electron mobility, and improved intermolecular interaction. In all-PSCs, PFY-3Se achieved an impressive PCE of 15.1 % with both high short-circuit current density of 23.6 mA cm⁻² and high fill factor of 0.737, and a low energy loss, which are among the best values in all-PSCs reported to date and much better than PFY-0Se (PCE=13.0 %). Notably, PFY-3Se maintains similarly good batch-to-batch properties for realizing reproducible device performance, which is the first reported and also very rare for the PSMAs. Moreover, the PFY-3Se-based all-PSCs show low dependence of PCE on device area (0.045–1.0 cm²) and active layer thickness (110–250 nm), indicating the great potential toward practical applications.

Light soaking (LS) is found to activate halide ion migration and significantly passivate the defects. By adding excessive PbI₂ in the precursor, the LS effect can be controlled and suppressed. An efficiency of 18.14% is achieved in all-inorganic CsPb(I_0.8Br_0.2)₃ perovskite solar cells with reduced LS time.

Abstract

Light soaking (LS) has been reported to positively influence the device performance of perovskite solar cells (PSCs), which, however, could be potentially harmful to the loaded devices due to the unstable output. There are very few reports on controls over the LS effect, especially in all-inorganic PSCs. In this study, a remarkable LS induced performance enhancement of CsPb(I_{1− x} Br _x )₃ based PSCs is presented. In situ grazing-incidence wide-angle X-ray scattering measurements quantize the temperature increase under illumination and reveal a radiative heating-induced lattice expansion. The device curing time is shortened with the increased Br/I ratio, evidently correlated with their distinct mobility and activation energy. It is suggested that LS could promote the migration of halide ions, giving rise to notable defect passivation and thus device improvements. Based on these understandings, an effective means is proposed to suppress the LS effect, which is to incorporate slightly over-stochiometric PbI₂ in precursor, and a champion PCE of 18.14% in all-inorganic PSCs with significantly reduced device curing time is obtained.

High-quality Sn–Pb perovskite thick films with well-packed, smooth, and pinhole/void-free features are formed via double-side crystallization tuning with a low-temperature space-restricted annealing process. The fabricated near-infrared photodetectors show a high and flat external quantum efficiency of ≈80% at 760–900 nm, remarkable responsivity of 0.53 A W⁻¹ and high specific detectivity of 6 × 10¹² Jones at 940 nm.

Abstract

Solution-processed narrow-bandgap Sn–Pb perovskites have shown their potential in near-infrared (NIR) photodetection as a promising alternative to traditional silicon and inorganic compounds. To achieve efficient NIR photodetection, high-quality Sn–Pb perovskite thick films with well-packed, smooth, and pinhole/void-free features are highly desirable for boosting the spectral absorption. Understanding the crystallization kinetics and tuning the crystallization are fundamentally important to reach such high-quality thick Sn–Pb perovskite films, and have been limitedly explored. Herein, an approach of double-side crystallization tuning through low-temperature space-restricted annealing in methylammonium-free Sn–Pb perovskite films with over 1 µm thickness is proposed. More specifically, through simultaneously retarding the crystallization in the top of precursor films and promoting the crystal growth of the bottom of precursor films, high-quality and block-like thick FA_0.85Cs_0.15Sn_0.5Pb_0.5I₃ perovskite films with improved crystallinity, preferred out-of-plane orientation, and reduced trap density are achieved. Finally, photovoltaic-mode Sn–Pb perovskite NIR photodetectors show a high external quantum efficiency of ≈80% at 760–900 nm, a recorded responsivity of 0.53 A W⁻¹, and a high specific detectivity of 6 × 10¹² Jones at 940 nm. This study offers the fundamental understanding of the crystallization kinetics of thick perovskite films and paves the way for perovskite-based emerging NIR photodetection and imaging applications.

A novel polymer acceptor PY2F-T with difluoro-monobromo end groups on monomer sub-units is synthesized, exhibiting extended absorption and stronger crystallinity compared to its non-fluorinated counterpart (PY-T). When employed in all-polymer solar cells, the PY2F-T based device yields an outstanding efficiency of 15.22% and retains a decent performance of 13.05% when processed under ambient conditions with an eco-friendly solvent (o-xylene, no additive).

Abstract

In this paper, a difluoro-monobromo end group is designed and synthesized, which is then used to construct a novel polymer acceptor (named PY2F-T) yielding high-performance all-polymer solar cells with 15.22% efficiency. The fluorination strategy can increase the intramolecular charge transfer and interchain packing of the previous PY-T based acceptor, and significantly improve photon harvesting and charge mobility of the resulting polymer acceptor. In addition, detailed morphology investigations reveal that the PY2F-T-based blend shows smaller domain spacing and higher domain purity, which significantly suppress charge recombination as supported by time-resolved techniques. These polymer properties enable simultaneously enhanced J _SC and FF of the PY2F-T-based devices, eventually delivering device efficiencies of over 15%, significantly outperforming that of the devices based on the non-fluorinated PY-T polymer (13%). More importantly, the PY2F-T-based active layers can be processed under ambient conditions and still achieve a 14.37% efficiency. They can also be processed using non-halogenated solvent o-xylene (no additive) and yield a decent performance of 13.05%. This work demonstrates the success of the fluorination strategy in the design of high-performance polymer acceptors, which provide guidelines for developing new all-PSCs with better efficiencies and stabilities for commercial applications.

The formation of a conformal oxide overlayer without damage to the perovskite layer is challenging. This study presents a highly dispersive ligand-off NiO (NiO_X) colloidal solution for n-i-p halide perovskite solar cells (HPSCs) using the designed solvent. The NiO_X overlayer shows outstanding charge extraction properties, and the NiO-HPSCs exhibit an efficiency of over 19.1% with excellent thermal stability.

Abstract

In n-i-p halide perovskite solar cells (HPSCs), the development of p-type oxides is one of the most noteworthy approaches as hole transport materials (HTMs) for long-term stability and mass production. However, the deposition of oxide HTMs through a solution process over the perovskite layer without damage to the perovskite layer remains a major challenge. Here, the colloidal dispersion of ligand-off NiO nanoparticles (NPs) to form the HTM overlayer on perovskite using appropriate solvents that do not damage the underlying perovskite layer is reported. Monodispersed NiO NPs are synthesized using oleylamine (OLA) ligands via the solvothermal method, and the OLA ligands are then removed to form ligand-off NiO NPs. Based on the Hansen solubility theory, appropriate mixed solvents are found for both the dispersion of NiO NPs without ligands and coating without perovskite damage. The colloidal dispersion form a compact and uniform NiO NPs layer of 30 nm thickness on the perovskite layer, allowing n-SnO₂/Halide/p-NiO HPSCs to be successfully fabricated. The HPSC shows a record power conversion efficiency under one sun illumination for an n-i-p oxide/halide/oxide structure and excellent thermal stability maintaining 98% of the initial efficiency for 580 h under 85 °C and 10% relative humidity condition.

The fast degradation of perovskite quantum dots (QDs) prevents the development of multicolor patterning technologies using these materials. Therefore, novel ligand systems for microsized EL device fabrication, which protect perovskite QDs from degradation through the binding kinetic control of surface ligands, are developed. The present system remains stable in various chemical environments, without critical deterioration of optical and electrical properties.

Abstract

Perovskite quantum dot (QD) light-emitting diodes (PeLEDs) are ideal for next-generation display applications because of their excellent color purity, high efficiency, and cost-effective fabrication. However, developing a technology for high-resolution multicolor patterning of perovskite QDs remains challenging, owing to the chemical instability of these materials. To overcome these issues, in this work, the generation of surface defects is prevented by controlling the ligand-binding kinetics using a stable ligand system (Stable LS). The crystalline reconstruction of perovskite QDs after addition of the Stable LS results in an ≈18% increase in their photoluminescence quantum yield in solution and it also improves the ambient stability of the perovskite QD solution. Moreover, the perovskite QDs with Stable LS can undergo cross-linking under UV irradiation. The tightly bridged perovskite QDs effectively prevent moisture-assisted ligand dissociation in film state due to the increased hydrophobicity and restricted movement of the cross-linked surface ligands. Thus, the cross-linked perovskite QD film shows improved chemical/environmental stability without substantial deterioration in optoelectrical properties. As a result, a white electroluminescent device with high resolution (≈1 μm) is successfully fabricated by inkjet printing using green and red perovskite QDs.

By fine-tuning the molecular electrostatic potential (ESP) distribution of photoactive materials, the morphology of donor:acceptor (D:A) photovoltaic films can be effectively adjusted. A large D:A ESP difference is required to assist charge generation, but too large ESP difference may result in additional nonradiative recombination loss and lead to hypermiscibility issues.

Abstract

Bulk heterojunctions comprising mixed donor (D) and acceptor (A) materials have proven to be the most efficient device structures for organic photovoltaic (OPV) cells. The bulk morphology of such cells plays a key role in charge generation, recombination, and transport, thus determining the device performance. Although numerous studies have discussed the morphology-performance relationship of these cells, the method of designing OPV materials with the desired morphology remains unclear. Herein, guided by molecular electrostatic potential distributions, we have established a connection between the chemical structure and bulk morphology. We show that the molecular orientation at the D-A interface and the domain purity in the blend can be effectively modulated by modifying the functional groups. Enhancing the D-A interaction is beneficial for charge generation. However, the resulting low domain purity and increased charge transfer ratio in its hybridization with the local excitation states lead to severe charge recombination. Fine-tuning the bulk morphology can give balanced charge generation and recombination, which is crucial for further boosting the efficiency of the OPV cells.

Nature Materials, Published online: 29 April 2021; doi:10.1038/s41563-021-01010-6

Nature Materials, Published online: 29 April 2021; doi:10.1038/s41563-021-00986-5

Publication date: 19 May 2021

Source: Joule, Volume 5, Issue 5

Author(s): Fujin Bai, Jianquan Zhang, Anping Zeng, Heng Zhao, Ke Duan, Han Yu, Kui Cheng, Gaoda Chai, Yuzhong Chen, Jiaen Liang, Wei Ma, He Yan

Two D–A copolymers, PBQ5 and PBQ6, are designed and synthesized based on difluoroquinoxaline (DFQ) units with different side chains. The organic solar cell (OSC) based on PBQ6 as donor and Y6 as acceptor achieves a high power conversion efficiency of 17.62%, which is one of the highest efficiencies for binary OSCs with a polymer donor and Y6 acceptor.

Abstract

Side-chain engineering has been an effective strategy in tuning electronic energy levels, intermolecular interaction, and aggregation morphology of organic photovoltaic materials, which is very important for improving the power conversion efficiency (PCE) of organic solar cells (OSCs). In this work, two D–A copolymers, PBQ5 and PBQ6, are designed and synthesized based on bithienyl-benzodithiophene (BDTT) as the donor (D) unit, difluoroquinoxaline (DFQ) with different side chains as the acceptor (A) unit, and thiophene as the π-bridges. PBQ6 with two alkyl-substituted fluorothiophene side chains on the DFQ units possesses redshifted absorption, stronger intermolecular interaction, and higher hole mobility than PBQ5 with two alkyl side chains on the DFQ units. The blend film of the PBQ6 donor with the Y6 acceptor shows higher and balanced hole/electron mobilities, less charge carrier recombination, and more favorable aggregation morphology. Therefore, the OSC based on PBQ6:Y6 achieves a PCE as high as 17.62% with a high fill factor of 77.91%, which is significantly higher than the PCE (15.55%) of the PBQ5:Y6-based OSC. The PCE of 17.62% is by far one of the highest efficiencies for the binary OSCs with polymer donor and Y6 acceptor.

Publication date: 19 May 2021

Source: Joule, Volume 5, Issue 5

Author(s): Deborah L. McGott, Christopher P. Muzzillo, Craig L. Perkins, Joseph J. Berry, Kai Zhu, Joel N. Duenow, Eric Colegrove, Colin A. Wolden, Matthew O. Reese

Magneto-electric (ME) correlation in two-dimensional organic–inorganic hybrid perovskites (2D-OIHPs) is demonstrated with a polar soft ferromagnetic system for the first time. The polarity of 2D-OIHPs is found in the nonmagnetic organic layers and also in the magnetic inorganic layers, where the ME response should be induced. Reflecting the soft magnetic nature, the ME-response is achieved by a low magnetic field.

Abstract

Two-dimensional organic–inorganic hybrid perovskites (2D-OIHPs) are attracting interest due to their structural tunability and rich functional characteristics, such as ferroelectricity and ferromagnetism. Here, we report the chiral-polar ferromagnetic 2D-OIHP copper chlorides with discernable electric polarization in the inorganic layers. In these systems, the magneto-electric (ME) correlation has been clearly observed by measuring a magneto-electric directional anisotropy (MEA), in which an optical absorption coefficient changes with reversal of the light propagating direction. We have found that the MEA can be induced by a low magnetic field of about 50 mT, reflecting soft magnetic nature. The present results suggest a new paradigm for designing functional ME multiferroics, which effectively couples magnetic and electric properties.

Publication date: 16 June 2021

Source: Joule, Volume 5, Issue 6

Author(s): Rui Sun, Wei Wang, Han Yu, Zeng Chen, XinXin Xia, Hao Shen, Jing Guo, Mumin Shi, Yina Zheng, Yao Wu, Wenyan Yang, Tao Wang, Qiang Wu, Yang (Michael) Yang, Xinhui Lu, Jianlong Xia, Christoph J. Brabec, He Yan, Yongfang Li, Jie Min